Automatic "woofer tester" at PE, what's inside?

[ChrisA]

I've seen this device advertised and a few people here say they work well. But I wonder what is really inside. Can't be much given the price.

My guess is that it is a sound card with a small <1W chip amp. But a signal (a frequency sweep) in the woofer then measure both the current and voltage and compare the relative phases.

If this is true I should be able to do the same thing with a cheap USB audio interface and some resistors.

[Pano]

You can, for example with Speaker Workshop.

But the WT3 is soooo easy and it works well. There is a USB soundcard inside and I suppose an ADC of some kind. It takes about 1 second to do the measurement.

[hitsware]

It's too fast for a sweep.
(the old one used a sweep)
I think it some way uses a pulse
and analyzes the response.
Also it needs no power amp
since traditional T/S is small signal.

[ChrisA]

Originally Posted by Pano

You can, for example with Speaker Workshop.

But the WT3 is soooo easy and it works well. There is a USB soundcard inside and I suppose an ADC of some kind. It takes about 1 second to do the measurement.

Yes I know it works. The question is "How, exactly?"

I have a brand new micro controller development system, looking for a easy but not trivial project and I thought a "no-computer-needed" speaker tester would be good, and way less than $99.

Actually I wanted to build the same kind of hand held meter for measuring complex impedance of radio antenna and transmission lines but audio frequency is always so much easier and so a better first project.

[c2cthomas]

Originally Posted by ChrisA

Actually I wanted to build the same kind of hand held meter for measuring complex impedance of radio antenna and transmission lines but audio frequency is always so much easier and so a better first project.

A handy tool to have around after a big bolt of lightning uses 'em as a discharge path!!!

The antennas and transmission lines that is. If a lightning strike eats the woofers ya got other problems (annnnnd yes it can eat your woofers - after it eats your amp).

[Pano]

Originally Posted by hitsware

It's too fast for a sweep.

The WT3 uses a fast sweep - for sure. You can hear it.

Originally Posted by ChrisA

Yes I know it works. The question is "How, exactly?"

Math. There is a USB DAC to generate the sweep. There is an ADC on the same line to measure the impedance - thru a voltage divider I suppose. A 1K resistor is supplied for calibration. The rest is in software. Speaker Workshop can do the same thing if you build a jig. Why not have a look at that?
I've run the WT3 software on other soundcards. It kinda works, but the calculated values are wrong. As to how the software works, I don't know.

[planet10]

The hardware is fairly trivial. It is more about the software. Here are the basics.

I use the DAC/ADC in my G4 PowerMac, a cable with a 1k resistor installed in the appropriate place (turns the amp into a current amp), a calibration resistor (i use 8 ohm, but 4/8/16 to match the driver would give a bit more accuracy), an early copy of FuzzMeasure, and a SS that calulates the derived parameters.

The original Smith & Larson WooferTester has similar HW to the PE clone, but i suspect the software is better (both are Windoz only so i have no direct experience)

dave

[hitsware]

> The WT3 uses a fast sweep - for sure. You can hear it.

It's not just a pop or click ?

[Pano]

No, not at all. A very fast sweep. No doubt whatsoever. Boooo-Weep! I've heard it dozens of times.
Sometimes Windows will not switch over to the WT3 device as the sound card and the sweep will come blasting thru whatever speakers are connected to the computer - loud! Never fails to make me jump.

The software just sends and receives from the default Windoze soundcard.

[ra7]

Hey, so if I have one of them jigs and a soundcard such as the m-audio transit, can I get woofer parameters to size boxes etc....?